The present invention relates to an image forming device, in which an image read from an original document to be processed is generated in units of a plurality of pixels, and a predetermined image process is provided to the image in parallel for the plurality of pixels, forms a duplicate image through a multi-beam output, and to an image processing method which the image forming device applies.
Conventionally, in an image forming device such as a facsimile device, an original document to be processed is read by a line sensor such as a CCD. Then, an image process, which adapts to the properties of an input/output device or the feature of the document, is provided to image data by a pixel unit. Thereby, both gradation and resolution of the image are improved. In this case, image data is synchronized with an image clock and input by a raster form. Moreover, image data, which is image-processed, is reproduced on a photosensitive drum by a laser writing and transferred on paper by an electronic photograph process. Thereby, the image is duplicated.
On the other hand, in a case of a high-speed copy reproduction, the rotation speed of a polygon mirror, which scans the photosensitive member by a laser beam, and a drive signal frequency of the laser must be increased in order to execute a duplication. However, there are limitations in the rotation speed of the polygon mirror such as power consumption of a motor, a laser pulse width modulation rate. To solve such a problem, there is proposed a system in which an image is written on a photosensitive member at high-speed by a multi-beam system for simultaneously scanning a plurality of lines by a plurality of lasers.
In the case of using the signal output system, which corresponds to the multi-beam, for simultaneously outputting image data of the plurality of lines, there was a problem as explained below:
Specifically, it is impossible to provide a predetermined image process to image data, which is input from an image input device such as a line sensor in a raster form in unit of a plurality of pixels. Moreover, a multi-beam output cannot be executed. In other words, image data input from the line sensor must be arrayed.
Also, it is necessary to select whether image data, which is input in the raster form in units of pixels from the image input device such as the line sensor, is simultaneously processed in parallel or processed at a high frequency in serial. However, there is a limitation in the high frequency image data process, because of the processing speed of the device. Therefore, it has been highly desired that the image processing is provided to the plurality of lines simultaneously in order to perform the high speed processing.
In the case of providing simultaneously parallel processing to image data, which is input in units of the plurality of lines in the raster form from the image input device such as the line sensor, there is a problem in which an image processing for obtaining a high quality of a duplicating image, such as a well-known error diffusion processing, cannot be performed.
Moreover, at the time of a multi-beam output, there is possibility that writing characteristics of the respective lasers will differ from each other due to variation of the lasers. As a result, correction between the beams is needed.